1. Field of the Invention
The present invention relates to an electronic device, simultaneously provided with heat dissipation medium and a heat insulation, used in motor-control circuits in general.
2. Description of the Prior Art
Circuits used for controlling motors in general, (including hermitic compressors for cooling), use electronic components that experience energy losses during operation resulting in heat generation by the components. There are various techniques of thermal coupling used today for providing transfer of this undesired heat to the environment, thereby avoiding overheating of the circuit, which may cause damage and/or reduction of the useful life of the electronic components.
The better the thermal coupling the better the transfer of heat between the electronic component, in which losses are generated, and the environment. So, the difference in temperature between the source of heat (electronic component with losses) and the environment, divided by the flow of transferred heat, represents the measure of the coupling in degrees Kelvin/Watt.
One of these techniques for providing a good thermal coupling of the electronic component with the environment consists in installing metallic elements thermally coupled to the electronic component, as for example, flaps. This metallic element has the function of a heat dissipator and is provided with a large area exposed to the surrounding air. In this way, it provides a good thermal coupling between the parts, significantly reducing the rise in temperature of the electronic component when the latter releases heat due to the Joule effect caused by the losses.
Although this is a quite effective and is a widely used way of providing a thermal coupling, it requires an attachment means, for example a screw, clip or the like, so that a physical coupling can be made between the electronic component and the dissipator, which requires a considerable physical space inside the equipment. Another drawback of this technique is that it requires added labor for mounting each component of the dissipator, entailing a high cost for this mounting process.
Another technique used for transferring heat between the electronic component and the environment are the so-called “heat tubes”, which use cooling fluids that transfer heat by phase change. This is a very efficient way of transferring heat, but it requires a special construction for the dissipator that contains this cooling fluid, thus making it very expensive. In addition, it requires a geometric form as well as a physical space adequate for mounting the parts together.
With regard to hermetic compressors, there are also techniques such as placing the heat dissipator coupled to the electronic components and in direct contact with the surrounding air. This technique requires an opening in the box that protects the equipment, resulting in complications for project, manufacture and mounting, and requiring effective solutions to avoid penetration of fluids into the equipment and to guarantee insulation between the parts electrically connected to the circuit and the dissipator, especially because the latter is accessible from the outside and may represent a risk to safety.
As described in document WO 972729, it is known to couple the electronic components to the carcass of the compressor, as the carcass region is close to the cooling-gas suction tubing that is at a quite low temperature due to the exit of the evaporator. In spite of facilitating the heat transfer, this solution requires physical contact between the electronic components and the carcass of the compressor, in addition to an efficient insulation, demanding the use of devices adequate for fixation and elaborate mounting solutions.
Document U.S. Pat. No. 5,060,114 describes the heat transfer of an electronic device by conduction effect. In this way, a shapeable silicone plate is molded so as to enclose the electronic device, removing the heat generated by the latter. This configuration has the disadvantage of dissipating the heat generated by the assembly of electronic components only when the heat has already exceeded the envelope of this device, that is to say, the silicone plate is not in direct contact with the components, but rather with the envelope that contains them. In this way, one increases the barriers that prevent heat escape in contact with the components.
Document U.S. Pat. No. 5,208,733 describes an encapsulation comprising a heat dissipator that supports a structural element. The dissipator comprises a metallic plate of considerable thickness, arranged on the electronic components. A layer of polymeric film is placed, by means of a vacuum process, onto the electronic components, which are arranged on a printed-circuit board that in turn is fixed on the structural element. A substance composed of silicone in the form of a gel is added to the envelope so as to fill the space existing between the metallic plate and the components. However, since this substance does not have electric-insulation characteristics, it does not come into direct contact with the electronic components nor with the printed-circuit board, and is thus limited to the contour defined by the polymeric film. This construction requires various associated processes during the manufacture of this envelope, which increase its cost due to the need for added labor.
Another disadvantage is that, in addition to the thick metallic plate, the envelope has another protecting layer, which makes the release of heat to the environment difficult. In order to overcome this drawback, a cooling system and the presence of connectors are described, which increases the cost and the physical space occupied by the envelope.